This invention relates to a system for controlling the level of ground water surrounding a swimming pool. More particularly, it relates to a system for balancing the respective levels of water in a pool and the adjacent ground for the protection of the pool.
In many areas of the country, the ground water level is relatively high and close to the surface of the ground. Also, during periods of heavy rain, excessive water can accumulate at or near the level of the ground, depending on local soil types and conditions. These phenomena can result in the ground water level rising to a level which can disrupt an in-ground pool installation. A similar result can occur if a pool is partially or completely emptied, something often necessary for its maintenance.
Where ground water rises to an elevation higher than the level of water in an in-ground pool, hydrostatic pressure can adversely affect the swimming pool structure. In the case of a swimming pool that has a vinyl liner, this condition may cause the liner to displace or float. In the case of concrete or other swimming pools, where exterior hydrostatic pressure becomes excessive it can disrupt the integrity of the swimming pool structure through shifting or dislodging of the wall and/or floor. Further, the pressure can cause the swimming pool to actually raise out of the ground.
The hydrostatic pressure is the result of a difference between the water level external to the swimming pool and its internal water elevation. It is apparent that a need exists for a system to safeguard against or minimize the adverse effects on a swimming pool due to hydrostatic pressure from elevated ground water levels.
This problem has long been recognized and a variety of approaches to its mitigation attempted. In, for example, U.S. Pat. No. 4,060,946, anchors are proposed to stabilize a pool. These "ground" anchors extend from the side of the pool shell or wall into the adjacent ground. Such anchors are said to reinforce the pool structure against the results of hydrostatic forces.
U.S. Pat. No. 4,227,266 discloses a different approach. There, collateral dewatering systems are installed in the ground around a pool. These systems limit the height of adjacent ground water by its direct removal from the environs of the pool. This controls the external hydrostatic pressure to which the pool is exposed.
This same U.S. Pat. No. 4,227,266 also appears to disclose a conventional cap valve at the bottom of some of its depicted pools. Such valves cap a pipe penetrating the pool bottom into the surrounding ground with a simple horizontally seating surface. They are known in the prior art and operate much like the common stopper in a bathroom sink.
Normally, such a cap valve has consisted of a horizontal metal disc attached to a vertical stem. About the bottom surface of the disc circumference there has been a flexible (e.g. rubber) gasket. This gasket seated on a corresponding and horizontal surface on or within the neck of a pipe penetrating into the ground. Such a cap valve was intended to close downwardly, preventing the outflow of water from a pool, while opening to allow a one-way influx of ground water into the pool whenever the hydrostatic pressure exterior of the pool exceeded that within the pool.
These prior art valves have several disadvantages. In particular, normally being mostly metallic, they corrode. Further, the gasket and opening are arranged such that the former frequently is dislodged or falls from its operating position. Lastly, these valves are readily clogged with leaves or other common pool debris and become stuck, often in an open position causing leakage from the pool.
An assembly containing such a prior art hydrostatic relief valve is described in U.S. Pat. No. 3,378,858. The valve, which again is not shown in detail, is located within a housing having a slotted cover.